signalr different "backends" for different hubs

### Is your feature request related to a problem? Please describe.
with the rise of blazor server side it would be a good idea to also have the ability to configure different "backends" for signalr.
i.e. consider the following:
ChatHub -> Redis
Blazor Memory (Stick Sessions)

thus it would make scaling a little bit easier, especially combining the two.

### Describe the solution you'd like
probably have something like:
`AddSignalR("Chat").AddStackExchangeRedis()`
and than:
`app.MapHub("/Chart", options => {}, "Chat");`

of course syntax can be different.

**Edit:**

maybe as an information, this is basically already possible "somewhat", but it's probably not known that much via:

```
.AddSingleton(typeof(HubLifetimeManager), typeof(RedisHubLifetimeManager)
```

of course this probably makes the syntax like: `AddSignalR("Chat").AddHubBackend(options => options.UseStackExchangeRedis()))` probably a good idea